1. Field of the Invention
The present invention relates to a digital signal processing for a TV camera, and more particularly to a digital signal processing system for a TV camera using a piece of solid image pickup element (for example, a charge coupled device; i.e. CCD) equipped with a color filter of mosaic/stripe type.
2. Description of the Prior Art
FIG. 15 shows a conventional example having a signal processing system using such an image pickup element. In the drawing, an image signal photoelectrically converted in a CCD 21 is subjected to a CDS processing (i.e.; a correlation double sampling processing), an AGC processing (i.e.; an automatic gain control), and a gamma correction in a circuit block 22. Then, the image signal is converted into a digital signal in an A/D converter circuit 23. The digitized signal is delayed by an amount of two horizontal scanning periods in a 2H delay circuit 24, and is fed in parallel to an LPF 25, a horizontal aperture processing circuit 26, a vertical aperture processing circuit 27, a false color suppression circuit 28, a white balance correction circuit 29, a picture plane division photometry circuit 30, and a brightness peak detecting circuit 31.
A brightness signal is separated in the LPF 25, and sent to an adder 32. On the other hand, an aperature correction component with respect to the brightness signal is produced in the horizontal aperture processing circuit 26, the vertical aperture processing circuit 27, an adder 33, a low brightness suppression processing circuit 34 and a highlight processing circuit 35 for applying corrections with respect to both a low-brightness and a high-brightness. In turn, the aperture correction component is added to the brightness signal in the adder 32.
The corrected brightness signal is sent to an D/A converter circuit 37 after having been applied an amplitude correction of a highlight portion in an auto-knee processing circuit 36.
On the other hand, a color signal outputted from the white balance correction circuit 29 is fed to a color separation time-sharing circuit 38 and, subsequently, added to a color difference matrix circuit 42 via a gain control circuit 39, an LPF 40, and a color difference clamp circuit 41. Then, thus line-sequentially obtained color signal becomes a regular color difference signal by being rearranged in a rearrangement process by use of a delay line, and sent to the D/A converter circuit 37.
The false color suppression circuit 28 detects an appearance of a false color, and suppresses the false color signal by controlling the gain control circuit 39 on the basis of the result of the detection.
Both the picture plane division photometry circuit 30 and the brightness peak detecting circuit 31 measure quantities relating to photo receiving condition on an image pickup surface. A micro computer 43 is connected to these picture plane division photometry circuit 30 and the brightness peak detecting circuit 31 through a data bus 44 to monitor and control the measuring results and conditions of above-described respective circuit blocks. Consequently, a brightness signal and a color signal, both processed in the optimum way, are outputted from the D/A converter circuit 37 after having converted into analogue signals therein.
In this manner, functions required for processing TV camera signals normally include various functions such as an aperture correction, a black level/highlight level setting, a direct current reproduction, a gamma correction, a noise removal etc.
Especially, since an aperture correction in a horizontal direction requires the signal delay equivalent to two horizontal scanning periods, it is noted that its signal processing order should be carefully determined.
Furthermore, the signals of image pickup element having a color mosaic filter, which is an object of the present invention, include brightness signals and color signals multiplexed together. Therefore, a function for separating both signals, and a function for rearranging separated line-sequential color signals simultaneously by use of the delay line are required. Furthermore, in this case, what kind of order should be applied to process these functions becomes the maximum problem in a system constitution.